Organic–Inorganic Halide Perovskite Formation: In Situ Dissociation of Cation Halide and Metal Halide Complexes during Crystal Formation

Organic–inorganic halide perovskites have shown great promise as photovoltaic materials that bridge the gap between facile and low-cost fabrication and exceptional solar cell performance. Manipulation of the stoichiometry and chemistry of the precursors is among the main techniques for controlling the structural properties of perovskite layer. Herein we report that when a precursor solution containing excess cation halides (CH3NH3I) is utilized for perovskite formation, in situ dissociation of cations (CH3NH3 +) occurs. The excess iodide ions­(I–) mostly participate in the formation of iodoplumbate complexes such as PbI3 – and PbI4 2–. It is shown that the released energy from the crystal formation reaction can dissociate the free CH3NH3I molecules and iodoplumbate complexes into smaller molecules such as CH3I and NH3. When the I– concentration in the precursor is increased, more complexes are formed and subsequently more dissociations occur. The produced components are mostly trapped in the perovskite crystals and can act as defects.